Dynamic response of HSS floorsComparative study of HSS floors •More than 10000 floor system design...
Transcript of Dynamic response of HSS floorsComparative study of HSS floors •More than 10000 floor system design...
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1Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Dynamic response of HSS floors
Anqi Chen
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2Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Content• Introduction
• Floor vibration analysis (FVA) method
• FVA tool
• Comparative study of HSS floors
• Conclusion
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3Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Steel Buildings and Vibration• Steel building designs generally meet criteria without
modification
• Even strictest criteria can be met with careful design
• Always important to assess vibration performance as remedial costs can be substantial
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4Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Introduction
• Response of steel floors to floor vibrations- RFCS HIVOSS project (Human Induced Vibration of Steel Structures)
- SCI P354 Design of Floors for Vibrations (updated)
• Two issues to be addressed for HSS floors:- lack of availability of analysis tools
- perception that HSS is worse than S355 floors in vibration response
• STROBE- A new analysis tool for floor vibration (FEM based)
- Study response of HSS floors (vs. S355 floors)
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5Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Traditional Practice• Serviceability criteria
• Primary & Secondary beams checked independently for minimum frequency of 3 Hz
• Analysis typically assumes self-weight and 10% of imposed load
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6Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Design of floors for Vibration• SCI P354 (2009)
www.steelconstruction.info
• Key publication for vibration design of floors in the UK
• Contains guidance for FE modelling, and a simple method
• Arcelor Mittal – Design Guide for Floor Vibrations
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7Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Human Induced Vibration• Approximated as
number of sine waves (harmonics)
• Pace frequency 1.8 Hz to 2.2 Hz
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8Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Vibration Response• Split into 2 parts: steady-state & transient
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9Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Vibration Response - Resonant• Lower frequency floors
• Continual force leads to response build-up
• Largest response when excitation frequency matches floor frequencies
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10Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Response Factor• Vibration is an issues of perceptions – varies from
person to person
• Depends on:▪ Direction of vibration relative to body
▪ Frequency of vibration
▪ Activity
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11Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Acceptance criteria
Place Multiplying factor for exposure to continuous vibration
16 h day 8 h night
Office 8
Shopping mall 4
Dealing floor 4
Stairs – Light use (e.g. offices) 32
Stairs – Heavy use (e.g. public buildings, stadia) 24
• Typical limiting values for response factors
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12Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Simple method• Simple method,
allows calculation using a spreadsheet
• Widely used – not every engineer has access to FE software
• Perception that it is extremely conservative for some designs
❑Fundamental frequency
❑Mode shape amplitude
❑Modal mass
(a) Secondary beam mode (b) Primary beam model
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13Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Finite element method• Rigid connections
• In vibration analysis, strains are not large enough to overcome friction
• Columns pinned at inflexion points
• Located at mid-height between floors for multi-storey construction
• Vertically restrained edge beams
• Cladding provides full vertical restraints, so the edge of clad buildings should be modelled as free in rotation but restrained in translation SCI office floor (Transient
Response Factor)
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14Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
www.steelconstruction.info Floor response calculator
http://bcsatools.steel-sci.org/FloorResponse/Default
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15Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Comparison of methods
• Frequency results close
• Floor response calculator & FE both show transient response is critical and values are close
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16Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Floor vibration analysis (FVA) tool• User defines
rectilinear floor system
• FE methods used to calculate the frequency and mode shapes
• SCI P354 used to calculate the response factors
CalculiX
(an open-source FE package)
Calculation engine
Pre- & post – processing
Online Beam Design Tool (DLL)
Floor response analysis P354 (Python libraries)
Floor Vibration Analysis (FVA) tool
User interface
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17Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
FVA tool
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18Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Validation• 28 test cases
• Compared against SCI floor response calculator
Steady state response factor
Transient state response factor
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19Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Comparative study of HSS floors• More than 10000 floor system design cases studied
• Design parameters (using typical values):▪ Steel grades (S355, S460 and S690)
▪ Bay arrangement (1x1 to 8x8)
▪ Span (primary and secondary beam)
▪ Slab (thickness and profile types)
▪ Loading
• Serviceability governed by deflection only
• Compare between functionally equivalent HSS and S355 floor systems
• Sensitivity to key parameters
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20Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Weight savingComposite floor
Histogram of primary beam weight saving due to steel strength upgrade
• Max weight saving▪ Long span
▪ Heavily loaded floors
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21Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Sensitivity studyExample: primary beam span
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22Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Sensitivity study• Vibration response of CSS and HSS floors show same
sensitivity to key floor design parameters
❑Fundamental frequency (f1): SSRF peaks at f1=8-9 Hz (resonance), TRRF dominates if f1 > 10 Hz
❑Total floor area↑ - vibration response↓
❑Slab height↑ - vibration response↓
❑Beam span ↑ - vibration response ↑ if in resonance
❑Beam span ratio (pri./sec.) ↑ - vibration response ↑
❑Floor load ↑ - vibration response ↓
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23Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Comparative study• Overall comparison of response factors
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24Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Comparative study• Fundamental frequency is the key
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25Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Comparative study• Weight saving vs vibration response factor ratio
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26Webinar Series: Structural Design of High Strength SteelsSTROBE: Stronger Steels in the Built Environment EU RFCS Research Project 743504
Conclusion• Floor vibration analysis (FVA) tool free to use
▪ Use more accurate FE method in SCI P354
▪ S355, HSS and Hybrid floor systems
• No special consideration for HSS floor system with respect to vibration response
• Using of HSS floor system does not always lead to higher vibration response
• Mitigation▪ Increase mass, stiffness or damping (i.e. deeper slabs)
▪ Alter layout (i.e. beam arrangement) during design phase
▪ Tie beams